I'm making collagen gels embedded with fibroblasts and they form well and normally. In the technical guidance, I'm told to adjust the pH of the collagen gel solution to neutral before I proceed to pipetting it into the wells of my plate. I skipped this step (as I couldn't find the pH test strips and it was my first go anyway- wanted to test if the gel set) and incubated the cell-gel overnight. The next day, the collagen gel contracted very well and I also had the chance to check the pH of the collagen solution (I prepared it in the same way again for testing) and it was just under pH 10. Once the gels are set, I add normal complete culture medium (5 ml) over the gel- DMEM4. Does anyone know if the pH is buffered to neutral by the culture medium and if not, what is the effect of the alkalinity on the cells?

Most medium is buffered by bicarbonate, which is not a particularly strong buffer - hence the colour change you get with dissolved CO2 in the incubator. I doubt it will be strong enough to bring the pH of the collagen matrix/medium to pH7 or thereabouts.

The alkalinity will affect how lipid behave and a range of cell processes that require ion transport - in other words, your cells will not be happy...